The present invention relates to an apparatus and method for error correction in a digital signal record/playback apparatus, and more particularly to an apparatus and method which interleaves two fields by frames so as to improve the burst error correction ability.
Generally, a digital video signal record/playback apparatus uses an encoding technique to compress and encode a great amount of picture information so as to efficiently transmit or store the picture information in digital form.
The encoded picture data is, however, disadvantageous in that errors which may occur during transmission, storage, reception or playback, deteriorate picture quality. In order to make up for this disadvantage of the encoding technique, an error correction encoding technique adds parity data to the picture information during the encoding, so as to correct the errors occurring during transmission, storage, reception or playback and obtain the original picture. Thus, errors are corrected by the usage of parity data.
However, among these errors, random errors occurring sporadically are easy to correct, but burst errors which occur in succession and form error groups are difficult to correct. The burst errors greatly affect picture quality. A product code is broadly used for burst error correction.
Referring to FIG. 1, in order to product-code the input video data (FIG. 2A) during coding, an outer encoder 2 adds parity data P.sub.0 -P.sub.5 in the column direction (FIG. 2B), and an inner encoder 4 adds parity data P.sub.0 -P.sub.7 in the row direction (FIG. 2C). Here, the length of outer code is 60 and the length of inner code is 54. An interleaving unit 3 connected between outer and inner encoders 2 and 4 arranges the video data which includes the horizontal parity data P.sub.0 -P.sub.5 added to its outer code, by fields that is, from left to right and from top to bottom as shown in the odd and even field maps of FIGS. 3A and 3B, and reads out the video data by bytes from top to bottom and from left to right in order for inner encoder 4 to add the parity data shown in FIG. 2C. A modulator 5 converts 8-bit picture information which is error-correction-encoded in inner encoder 4 into N-bit data (10bits). A recording amplifier 6 amplifies the N-bit data to record it on a recording medium 7 such as tape.
Here, FIG. 4 illustrates a format wherein error-correction-encoded picture information is recorded on tape.
As shown in FIG. 4, one field is recorded onto four tracks of a tape. Data A0,0 to A15,14 is recorded on the first track of an odd field, data A0,15 to A15,29 is recorded on the second track of the odd field, data A0,30 to A15,44 is recorded on the third track, and data A0,45 to A15,59 is recorded on its fourth track. Data B0,0 to B15,14 is recorded on the first track of an even field, data B0,15 to B15,29 is recorded on the second track of the even field, data B0,30 to B15,44 is recorded on the third track, and data B0,45 to B15,59 is recorded on its fourth track.
Then, the recorded data is amplified by a reproducing amplifier 8, and a demodulator 9 converts the 10-bit data back into 8-bit serial data during recording. An inner decoder 10 decodes the data output from demodulator 9, and corrects the errors within its error correction ability. The inner decoder adds an error flag to the data having errors outside the range of error correction, and supplies a de-interleaving unit 11 with the result. The de-interleaving unit 11 re-reads out by fields the odd field data A0,0 to A15,59, and even field data B0,0 to B15,59 which is recorded onto four tracks as shown in FIG. 4, so as to output the read-out data to an outer decoder 12.
According to the error flag, outer decoder 12 re-corrects the outer codes of data from de-interleaving unit 11, and outputs the re-corrected outer codes.
An error correction apparatus using a product code is disclosed in Japanese laid-open patent publication No. sho 64-30344. During outer decoding in normal playback and when outer decoding is not performed in high-speed playback, the No. sho 64-30344 error correction apparatus inner-decodes by selecting a decoding algorithm corresponding to each case. This reduces the uncorrectable errors occurring due to inner-code error correction.
However, the error correction ability of the aforementioned error correction apparatus is within A0,0 to A15,5 that is, 54.times.16.times.6 bytes per track of a field so that errors outside of the range cannot be corrected. In other words, according to this apparatus, since one field of data is successively recorded onto four tracks of a tape, when a burst error over 54.times.16.times.6 bytes occurs, it cannot be efficiently dispersed. This weakened error correction ability deteriorates picture quality.